The February 1956 meeting of the governing body of the Communist Party of the Soviet Union (CPSU) that formally denounced Stalinism. Theoretically the ruling body of the CPSU, the party congress was usually a pro forma, ceremonial event. However, the Twentieth Party Congress, held in Moscow, was a watershed in the history of international communism and the Cold War. In his celebrated so-called secret speech, First Secretary of the CPSU Nikita Khrushchev revealed to dumbstruck delegates that the late Soviet leader Josef Stalin was a bloodthirsty criminal responsible for systematic killing and mass terror instead of a wise and beneficent ruler to be adored and idolized.

Khrushchev delivered his speech in the very early hours of 25 February 1956 to a closed session of the congress from which all foreign delegates had been excluded. Khrushchev himself was largely responsible for the decision to issue a stinging denunciation of Stalin's rule. It had been opposed by the overwhelming majority in the presidium, who did manage to prevent the incorporation of the speech into Khrushchev's formal, open report. Khrushchev limited his comments to Stalin's use of terror against "loyal communists" after 1934. Revelation of Stalin's "violations of socialist legality" (the term "crimes" was avoided) was restricted to abuses against the party elite. Khrushchev went on to speak approvingly of Stalin's struggle against Trotskyist and Bukharinist "oppositionists" in the 1920s and during the industrialization drive. Khrushchev did not question the one-party system, land collectivization, or the command economy, all of which he sought to preserve.

In spite of these limitations, the speech was a political bombshell, exposing the mechanism of terror and the system of arbitrary rule that had dominated the Soviet Union for thirty years. Khrushchev employed dozens of government papers and a wealth of detail to document the brutal character of Stalin's reign of terror. One such document, which Khrushchev read aloud, was a letter from a Politburo member whose spine was broken by his interrogator. Khrushchev convincingly demonstrated that the history of the CPSU under Stalin consisted of a pattern of criminal acts, unlawful mass deportations of non-Russian peoples, political errors such as the break with Josip Broz Tito's Yugoslavia, inept leadership, the methodical falsification of history directed by Stalin himself, and the abandonment of Leninist principles of collective leadership in favor of the cult of personality. In short, Khrushchev entirely debunked the mystical aura that surrounded Stalin.

The allegedly secret speech, deliberately leaked to a Western correspondent through a former Komitet Gosudarstvennoi Bezopasnosti (KGB) official, has long overshadowed the rest of the Twentieth Party Congress's proceedings. Yet Khrushchev's 14 February open speech on peaceful coexistence with the West was almost as significant. He jettisoned the classic thesis of Marxism-Leninism, namely that war with the West was inevitable as long as capitalism survived. He also called for nonviolent competition between capitalism and communism; argued that communism would inevitably prevail over capitalism because it was a fairer system; acknowledged that there were different transitional forms from capitalism to socialism, including the parliamentary route of free elections; and insisted that the Soviet Union did not seek to export revolution.

The implications of Khrushchev's secret and public speeches reinforced each other with overwhelming effect. On the one hand, Stalin's authoritarian methods were discredited; on the other hand, a peaceful, parliamentary road to socialism was acclaimed. For authoritarian communist parties such as those in Albania, the People's Republic of China (PRC), and the Democratic People's Republic of Korea (DPRK, North Korea), this was heresy, but for others, such as Poland's, it was liberating. The nation most profoundly affected by the Twentieth Party Congress was Hungary. Within the Hungarian Workers' Party, a movement seeking greater democratization and national independence soon gathered momentum. In July 1956, Hungary's first secretary of the Central Committee, Mátyás Rákosi, was dismissed. In early October, László Rajk and other Hungarian victims of the 1949 Stalinesque trials were paid tribute, and in late October the new regime of Imre Nagy replaced that of Ernő Gerő. Unfortunately, however, the Budapest uprising of 1956 was soon quashed by the Soviet Army.

The Twentieth Party Congress did not reverberate only in Eastern Europe. It also shattered the chimera of ideological continuity between 1917 and 1956. In so doing, it created the possibility for a new, more independent direction for world communist movements.